Relationship between scale growth checks, circuli formation rate and somatic growth in Rutilus rutilus (L.) a fish farm-reared cyprinid
Check formation on scales of roach Rutilus rutilus was examined during their production cycle at a fish farm in England through analysis of circuli patterns. Regular check formation was associated with the movement of fish from one type of grow-out facility to another; this resulted in a sudden shift in growth rate and the formation of a new check. As these had the characteristics of annual marks, their formation potentially invalidates their use as structures to determine the age of individuals during recapture events that may follow their introduction to the wild. At low growth rates, the number of circuli was constant throughout the year; this situation changed when fast growth rates were achieved. Five methods of backcalculation were also validated. When the proportionality between the body length and scale radii was weak, backcalculation methods were poor in determining length at check formation.